feat(post): RPM creation for Java application

Author: SyntaxRules

_posts/2017-10-12-Creating-an-rpm-for-java-application.md

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+# Creating an RPM for a Java Application
+
+Herein lays an example of creating an RPM for Java Applications with Gradle.
+
+## Overview
+
+Creating a RPM that can run a Java application requires two steps. The first is to create a jar file that can be ran. The second is to create a RPM that installs this jar file and its dependecies on the target system. This certainly isn't the only way to do this, but it seems to be the easiest.
+
+## Creating a runnable JAR file
+
+There are many resources out there for creating a runnable JAR file. The Gradle application plugin will even create a jar for you out of the box. A regular JAR file isn't enough, you need a JAR file that also contains all of it dependecies. This kind of Jar file is often called a fat or uber JAR because of these extra dependecies. Luckly for us, a gradle plugin called **Shadow** takes care of this.
+
+You can add shadow to your gradle file by adding the following lines to the beginning of your *.gradle file:
+
+```
+plugins {
+    id 'com.github.johnrengelman.shadow' version '2.0.1'
+}
+```
+
+Assuming you have the rest of your gradle set up to run your java application, you can immediately use Shadow after adding this line. Shadow adds a few gradle tasks, the one we are interested in is `gradle shadowJar`. See `gradle tasks` for all the exposed tasks shadow introduces.
+
+Try it out. Run `gradle shadowJar` and look in your `build/libs` folder for the newly generated JAR file. you can run this jar file with `java -jar somefile.jar`.
+
+## Creating an RPM package
+
+To create an RPM package I used the `ospackage` gradle plugin. The plugin can be added to your gradle file by editing the plugins field we added in the last section. Modify it to look like:
+
+```
+plugins {
+    id "nebula.ospackage" version "4.4.2"
+    id 'com.github.johnrengelman.shadow' version '2.0.1'
+}
+```
+
+Unlike the shadow plugin, ospackage requires the user to apply this plugin. I did so by adding the following line:
+
+```
+apply plugin: "nebula.ospackage"
+```
+
+ospackage doesn't know how to create an RPM specific to your project, it requires some extra configuration. See the [RPM packaging guide](http://rpm-guide.readthedocs.io/en/latest/rpm-guide.html) for information on how to configure it. Give it your best shot, here Is what I came up with:
+
+```
+ospackage {
+    release '1.el7'
+    user 'foo'
+    permissionGroup "foo"
+    summary 'Testing that RPMs can be created and ran using Java.'
+
+    arch 'X86_64'
+    os 'LINUX'
+    type 'BINARY'
+
+    from (shadowJar.outputs.files) {
+        into "/opt/test"
+    }
+
+    from("scripts/rpmtest") {
+        into "/opt/test"
+        fileMode = 0755
+    }
+
+}
+
+buildRpm {
+    requires("some-dep", "0.2.7", GREATER | EQUAL)
+    directory("/opt/test", 0755)
+    link("/usr/bin/rpmtest", "/opt/test/rpmtest")
+}
+buildRpm.dependsOn(shadowJar)
+```
+
+There are a few things to point out in my configuration. First buildRpm.dependsOn(shadowJar). This is required so you can copy the JAR that shadow creates into your RPM. Second, I had to create a script to acutally run my fat JAR. This script is really simple, it just runs:
+
+```
+#!/usr/bin/env sh
+
+java -jar /opt/test/rpmtest-*
+```
+
+After I finished this configuration I tested this approach by installing the rpm and attempting to run it. After a few permissions tweaks and trial and error, I got it running with the solution above.
+
+## References
+
+- [Creating Unix Services and RPM/DEB Packages with Spring Boot and Gradle](https://www.ccampo.me/java/spring/linux/2016/02/15/boot-service-package.html)
+- [Ccampo Example Application](https://github.com/ccampo133/boot-daemon-demo)
+- [Gradle ospackage RPM documentation](https://github.com/nebula-plugins/gradle-ospackage-plugin/wiki/RPM-Plugin)
+- [Shadow (fat) jar documentation](http://imperceptiblethoughts.com/shadow/)
+- [RPM packaging guide](http://rpm-guide.readthedocs.io/en/latest/rpm-guide.html)